The X-ray tube is, for example, structured, as described in patent document 1 (JP-A-2001-319607), such that a cathode supplying an electron and an anode irradiating the electron so as to generate an X-ray are received within a glass vessel formed by a glass, an inner side of the glass vessel is formed in a vacuum condition, the cathode and the anode or the cathode and a ground potential conductor are insulated by the vacuum and the glass, and an outer side of the glass vessel is filled with an insulating fluid.
In the X-ray tube having the structure mentioned above, a weak position in view of an insulation is an interface between the glass and the vacuum. It has been known that an insulating performance is significantly lowered in the case that a gas component is adsorbed to a vacuum side interface of the glass, or that a conductive dust is attached. In this case, in conventional, there has been applied a conditioning process of mirror finishing an inner surface of the glass vessel, sufficiently cleaning by means of a solvent or the like and thereafter applying a voltage having a limited current via a high resistance while exhausting the inner side of the glass vessel so as to gradually improve a withstand voltage performance. The withstand voltage performance of the vacuum portion and the inner surface of the glass vessel is regulated to a necessary state in accordance with these processes, and the insulation of the X-ray tube is secured by charging the insulating fluid in the outer side of the glass vessel.
On the other hand, although it is not a technique relating to the X-ray tube, there has been reported a matter that a creepage flashover voltage of a glass spacer supporting a high-voltage conductor can be improved by polishing a surface of the glass spacer and forming a concavityand convexity having an average surface roughness between 0.003 and 3.07 μm, in order to improve the insulating performance of the glass insulation material within the vacuum container (non-patent document 1 (“Flashover Characteristics Of A Glass Spacer In Vacuum” Institute of Electrical Engineers National Convention in 2003, in Sendai on 2003 Mar. 17 to 19, First Edition 1-076, page 102)).